If you put a Puch kit on a Tomos, you _might_ need to drill out the holes that the cylinder studs go through; Tomos uses M7 studs, but Puchs use M6. Also, I'd beware of anything with really big transfers -- maybe it's just me and my A3's, but it seems like there's more room to grind out the case transfers on the Puch cases than there is on the Tomos cases.
Also, where are you getting all this information about what's good and bad? I have never heard anyone here complain about 1-ring pistons on mopeds, and I don't hear a lot about any of the Tomos kits being particularly bad. I mean, I guess I don't look at the Tomos kit stuff much, but it isn't like there's a thread a day about how XYZ kit sucks.